1. Technical Field
The present invention relates to a gas laser oscillator that oscillates laser using laser gas as a medium.
2. Description of the Related Art
It is important for a gas laser oscillator that oscillates laser using laser gas as a medium to maintain sealability of a gas container for containing the laser gas. For example, in a less sealable gas container, air or moisture is mixed into the laser gas, whereby a composition of the laser gas is changed. As a result, a desired laser output may not be obtained, which leads to poor processing or increased processing time. Further, impedance matching cannot be achieved between a laser power supply side and a discharge load side (matching units, electrodes, discharge tubes, and laser gas in a discharge space), so that overcurrent may flow into the laser power supply, or overvoltage may be applied to the discharge tubes. This may result in breakdown of the power supply unit or the discharge tubes, or alarm stop of the gas laser oscillator in response to abnormality detection.
JP-U-H09-000405 discloses a gas laser oscillator provided with a gas leakage detection device capable of detecting laser gas leakage by comparing a gas pressure before turning off the gas laser oscillator with a gas pressure at a time when it is turned on next. This patent literature also discloses the use of a temperature sensor for measuring a laser gas temperature in order to accurately measure the gas pressures.
JP-A-2008-153281 discloses a gas laser oscillator configured to determine abnormality of a laser gas composition on the basis of a current value output from a power supply unit in a state where a laser gas pressure is lower than that during normal operation.
JP-A-2008-004773 discloses a gas laser oscillator provided with a laser gas determination means that determines the kind of a laser gas on the basis of a relationship between laser gas pressure and electric power supplied to a turbo blower for circulating the laser gas, and an abnormality determination means that determines abnormality of the gas laser oscillator according to a result of the determination.
The known technique described in JP-U-H09-000405 cannot estimate sealability of the gas container unless the gas laser oscillator is stopped for a sufficiently long period of time, and also cannot estimate reduction in the sealability that gradually proceeds along with the use of the container, such as O-ring deterioration. In addition, a temperature sensor is needed to accurately measure the gas pressures, which has been a factor for increased cost.
The known techniques described in JPA-2008-153281 and JP-A-2008-004773 need to exhaust laser gas for each measurement and then supply laser gas again. This increases laser gas consumption, resulting in increased cost. In addition, when the degree of reduction in the sealability of a gas container is very small, an amount of change in a DC current value or an electric power of the turbo blower corresponding to the degree thereof is small, so that measurement error cannot be ignored. Due to this, change in the gas laser composition may not be accurately determined.
JP-A-2011-222586 and JP-A-2014-053423 disclose a technique in which, in a gas laser oscillator configured such that a voltage corresponding to a power supply output command increasing in a stepped manner is applied to discharge tubes, it is determined whether or not discharge has been started in the discharge tubes on the basis of a ratio of a voltage change in the discharge tubes to a power supply output command.
The present inventor has focused on the fact that when a laser gas composition changes, i.e., sealability of the gas container is reduced, discharge occurs less easily, increasing an amount of time needed to start discharge (hereinafter referred to as “discharge start time”) and has proposed a gas laser oscillator capable of estimating sealability of the gas container on the basis of the discharge start time.